<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>盒子阴影</title>

        <style>
            * {
                margin: 0;
                padding: 0;
            }

            #app {
                width: 200px;
                height: 200px;

                margin: 40px;

                border: 1px solid purple;
            }

            #app:hover {
                box-shadow: 10px 10px 5px 5px pink,-10px -10px 5px 5px gray;
            }
        </style>
    </head>
    <body>
        <div id="app"></div>
    </body>
</html>